One of the top pass rushers in this year's free agent class, Avril has accumulated 40 sacks over his five-year career, which had all been spent with the Detroit Lions. He had a career-high 11 sacks in 2011.

Avril is the Seahawks' second high-profile addition in the past three days. Seattle completed its trade for wide receiver Percy Harvin on Tuesday.

Earlier in the day, the Lions signed defensive lineman Jason Jones, formerly of the Seahawks.